An airport in Tampa, Florida, has had to temporarily close its runways to keep up with Earth's magnetic north pole, which is drifting toward Russia at a rate of 40 miles per year.

Fox News reports that the international airport was forced to adjust the signs on its busiest runway Thursday because pilots depend on the magnetic fields to navigate. The runway will be closed until Jan. 13, and will re-open with new taxiway signs that indicate its new location on aviation charts, the Tampa Bay Tribune reports.

Paul Takemoto, a spokesman for the FAA, says the Earth's magnetic fields are constantly in flux -- but rarely so much so that runway signage needs to be changed. "You want to be absolutely precise in your compass heading," he told Fox. "To make sure the precision is there that we need, you have to make these changes."

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"The Earth's poles are changing constantly, and when they change more than three degrees, that can affect runway numbering," FAA spokesperson Kathleen Bergen told Fox News. It's unclear whether any other airports will have to adjust their runways.

Earth's magnetic field, which still flummoxes those who study it, "is thought to be generated deep inside the planet," LiveScience writer Jeanna Bryner explains. "An inner core of solid iron is surrounded by an outer core of molten iron. They rotate at different rates, and the interaction between the regions creates what scientists call a 'hydromagnetic dynamo.' It's something like an electric motor, and it generates a magnetic field akin to a giant bar magnet."

Sometimes, the poles completely flip -- and presumably when that happens, many bigger changes are afoot than modest tweaks to airport signs. The last time the planet experienced a polarity flip was 780,000 years ago.